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AAPG Bulletin


AAPG Bulletin, V. 87, No. 11 (November 2003), P. 1823-1846.

Copyright copy2003. The American Association of Petroleum Geologists. All rights reserved.

Deformation and the timing of gas generation and migration in the eastern Brooks Range foothills, Arctic National Wildlife Refuge, Alaska

T. M. Parris,1 R. C. Burruss,2 P. B. O'Sullivan3

1U.S. Geological Survey, Box 25046, M.S. 939, Denver Federal Center, Denver, Colorado; present address: Petro-Fluid Solutions, LLC, 608 North Sheridan Ave., Loveland, Colorado, 80537; email: [email protected]
2U.S. Geological Survey, National Center M.S. 956, 12201 Sunrise Valley Drive, Reston, Virginia, 20192; email: [email protected]
3Syracuse University, Department of Earth Sciences, Syracuse, New York; present address: Apatite to Zircon, Inc., 1521 Pine Cone Road, Moscow, Idaho, 83843; email: O'[email protected]


Marty is founder of Petro-Fluid Solutions, which applies petrographic, stable isotope, and fluid inclusion analyses to reservoir and structural diagenesis problems. Previously, he held a postdocorate position with the U.S. Geological Survey (1999–2002) and research geologist at ARCO (1997–1999). Marty received degrees from the University of California Santa Barbara (Ph.D.), Texas Christian University (M.S.), and Tennessee Tech University (B.S.).

Robert C. Burruss received a B.S. degree in chemistry from Juniata College (1971) and a Ph.D. in geology from Princeton University (1977). He worked for Gulf Oil until 1984 and then moved to the U.S. Geological Survey. He works on oil and gas migration, and currently, he is chief of the project, "Assessment of Geologic Reservoirs for Carbon Sequestration."

Paul O'Sullivan is vice president at Apatite to Zircon, specializing in apatite and zircon fission-track thermochronology. He earned his M.S. degree in geology from the University of Alaska in 1989, and his Ph.D. in geology from LaTrobe University in 1994. Since 1988, he has been actively researching the post-Jurassic thermal history of the Arctic North Slope of Alaska.


We would like to thank Dave Leach and Greg Meeker for the use of fluid inclusion and microbeam facilities at the U.S. Geological Survey (Denver). Thanks to Bill Christiansen (U.S. Geological Survey, Denver) and Al Hofstra (U.S. Geological Survey, Denver) for acquiring the stable isotope data. Discussions with and reviews by Neil Fishman (U.S. Geological Survey, Denver) and Ken Bird (U.S. Geological Survey, Menlo Park) provided valuable perspective and improvements to the manuscript. Thanks to AAPG Bulletin reviewer Richard Swarbrick for comments and suggestions that improved our interpretation of overpressure and its evolution.


Along the southeast border of the 1002 Assessment Area in the Arctic National Wildlife Refuge, Alaska, an explicit link between gas generation and deformation in the Brooks Range fold and thrust belt is provided through petrographic, fluid inclusion, and stable isotope analyses of fracture cements integrated with zircon fission-track data. Predominantly quartz-cemented fractures, collected from thrusted Triassic and Jurassic rocks, contain crack-seal textures, healed microcracks, and curved crystals and fluid inclusion populations, which suggest that cement growth occurred before, during, and after deformation. Fluid inclusion homogenization temperatures (175–250degC) and temperature trends in fracture samples suggest that cements grew at 7–10 km depth during the transition from burial to uplift and during early uplift. CH4-rich (dry gas) inclusions in the Shublik Formation and Kingak Shale are consistent with inclusion entrapment at high thermal maturity for these source rocks. Pressure modeling of these CH4-rich inclusions suggests that pore fluids were overpressured during fracture cementation.

Zircon fission-track data in the area record postdeposition denudation associated with early Brooks Range deformation at 64 plusmn 3 Ma. With a closure temperature of 225–240degC, the zircon fission-track data overlap homogenization temperatures of coeval aqueous inclusions and inclusions containing dry gas in Kingak and Shublik fracture cements. This critical time-temperature relationship suggests that fracture cementation occurred during early Brooks Range deformation. Dry gas inclusions suggest that Shublik and Kingak source rocks had exceeded peak oil and gas generation temperatures at the time structural traps formed during early Brooks Range deformation. The timing of hydrocarbon generation with respect to deformation therefore represents an important exploration risk for gas exploration in this part of the Brooks Range fold and thrust belt. The persistence of gas high at thermal maturity levels suggests, however, that significant volumes of gas may have been generated.

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